Dry-compressing pumps are becoming ever more important in industrial compressor technology. Due to increasing obligations with regard to environmental regulations and rising operating and disposal costs, as well as greater requirements with regard to the purity of the delivery medium, known wet-running pump systems, such as liquid ring machines, rotary vane pumps and oil or water-injected screw compressors, are replaced with dry-compressing pumps with increasing frequency. Dry screw compressors, claw pumps, diaphragm pumps, piston pumps, scroll machines, as well as Roots pumps, are among these dry-compressing machines. However, what these machines have in common is that they still do not meet today's requirements relating to reliability, ruggedness, constructional size and weight, while at the same time having a low price level and satisfactory compressor efficiency.
Known dry-compressing screw spindle pumps suggest themselves for improving this situation, because, like typical dual-shaft displacement machines, they obtain a high compression capacity simply by achieving the required multi-stage property as so-called “delivery threads” by a series arrangement of several sealed working chambers through the number of loops per compressor rotor in an extremely uncomplicated manner. Moreover, the contactless rolling of the screw spindle rotors that rotate in opposite directions enables an increased rotational speed of the rotors, so that the nominal suction capacity and the volumetric efficiency are increased at the same time, relative to the design size.
A simple rotor cooling system is described for a dry-compressing screw spindle pump in International Patent Application Publication No. WO 00/12899, wherein a coolant, such as oil, is introduced into a conical rotor bore in each rotor, in order to permanently dissipate a part of the compression heat produced during the compression process. Pursuing this approach in International Application No. PCT/EP2008/068364, the coolant is used with an internal (oil) pump, for cooling the pump housing in order to dissipate in a coolant circuit the absorbed amounts of heat from the compression of the delivery medium and the power dissipation via a separate heat exchanger in such a way that the clearance values between the rotor pair and the surrounding pump housing are maintained for all operating states.
For achieving greater compressor powers however, there is still no efficient and inexpensive solution to minimize the pump-specific forces in the axial and radial direction and minimize the compressor power values efficiently, reliably, robustly and inexpensively. Until now, dry-compressing screw compressors having two screw compressors with an intermediate gas cooling system still must be used for higher pressure values, for example, 11 bar as absolute pressure, with an unsatisfactory efficiency at the same time. Accordingly, the corresponding total expenditure is a constant nuisance, both with regard to the purchase of an intermediate gas cooling system additionally required due to two-compressor machines, as well as with regard to operation, due to the, on the whole, modest efficiency. This is desired to be improved significantly.